Field of the Invention
The present invention relates to formulations comprising at least one low molecular weight hydridosilane and at least one hydridosilane oligomer, to processes for preparation thereof and to the use thereof, especially for production of silicon-containing layers.
Discussion of the Background
Hydridosilanes or oligomers thereof have been described in the literature as possible reactants for the production of silicon-containing layers.
Hydridosilanes are understood to mean compounds containing essentially only silicon and hydrogen atoms and having fewer than 20 silicon atoms. Hydridosilanes may in principle be gaseous, liquid or solid and are—especially in the case of solids—essentially soluble in solvents such as toluene or cyclohexane or in liquid silanes such as cyclopentasilane. Examples include monosilane, disilane, trisilane, cyclopentasilane and neopentasilane. Hydridosilanes having at least three or four silicon atoms may have a linear, branched or cyclically (optionally bi-/polycyclic) structure having Si—H bonds, and can preferably be described by the respective generic formulae SinH2n+2 (linear or branched; with n=2-20), SinH2n (cyclic; with n=3-20) or SinH2(n−i) (bi- or polycyclic; n=4-20; i={number of cycles}−1).
Processes for preparing hydridosilanes having at least 3 silicon atoms are disclosed, for example, in U.S. Pat. No. 6,027,705 A. A thermal process for preparing oligomers of hydridosilanes is disclosed by WO 2011/104147 A1. In addition, WO 2012/041837 A2 discloses a process for preparing higher hydridosilane compounds, in which a lower hydridosilane compound is converted thermally in the presence of a hydridosilane polymer of at least 500 g/mol.
Silicon-containing layers can be deposited from the gas phase in vacuum chambers, for example via PECVD. Gas phase processes, however, are technically complex and often do not lead to layers of the desired quality. For this reason, liquid phase processes are often preferred for production of silicon-containing layers.
The prior art describes various hydridosilane-containing formulations. For example, U.S. Pat. No. 5,866,471 A discloses formulations containing semiconductor precursors, with which semiconductor layers can be produced. The usable semiconductor precursors also include hydridosilanes. WO 2008/137811 A2 also discloses compositions containing one or more semiconductor precursors which are selected from a group and include (poly)silanes. US 2009/0215219 A1 also discloses a process for producing a semiconductor layer, in which a liquid coating composition containing silicon atoms is applied to a substrate. The coating composition may contain a silane polymer, which may be a polyhydridosilane. US 2010/0197102 A1 discloses solutions containing a compound which is preferably a silane having four to nine silicon atoms. Coating compositions containing a polysilane are also described in EP 1 357 154 A1. EP 1 640 342 A1 further discloses silane polymers having a weight-average molecular weight of 800 to 5000 g/mol, which can be used for production of silicon-containing films. JP 2008-270603 A and JP 09-45922 A also disclose coating compositions for production of silicon-containing films, in which various silicon compounds can be used as precursors. Mixtures of various hydridosilane precursors are not disclosed in the literature references cited.
JP 2004-134440 A discloses coating compositions for production of silicon-containing films, which contain various silane compounds and cyclic silanes. EP 1 085 579 A1 and EP 1 087 428 A1 also disclose coating compositions for production of silicon-containing layers, in which two silicon precursors are used. These are a cyclic silicon compound and a doped silicon compound. JP 2000-031066 A discloses liquid coating compositions containing a hydridosilane of the generic formula SinH2n+2 or SinH2n or mixtures of the two. DE 10 2010 030 696 A1 likewise discloses liquid coating compositions which may include hydridosilanes as silicon precursors.
Coating compositions containing exclusively low molecular weight hydridosilanes as silicon precursor have disadvantages in the production of silicon-containing layers. More particularly, they are unsuitable for the production of very thin silicon-containing layers (layers having a thickness of max. 25 nm), since the low molecular weight material vaporizes before it can crosslink at typical conversion temperatures. For this reason, coating compositions containing hydridosilane oligomers having high molecular weights are often used as alternatives. These high molecular weight hydridosilane oligomers are suitable in principle for production of silicon-containing layers, but they have the disadvantage of dissolving only sparingly in organic solvents, which leads to disadvantages of the layers produced therewith. For this reason, there exist, in the prior art, coating compositions including not only high molecular weight hydridosilane oligomers but also low molecular weight hydridosilanes, the latter functioning as solvents.
The prior art discloses coating compositions for production of silicon-containing layers, containing a hydridosilane oligomer in a mixture with a cyclic hydridosilane (Masuda et al., Thin Solid Films 520 (2012) 5091-5096). Corresponding coating compositions containing a cyclic hydridosilane, however, have the disadvantage that they are stable only at high concentrations of cyclic hydridosilanes. At low concentrations of cyclic hydridosilanes, the formulations rapidly become cloudy and are then unsuitable for production of high-quality silicon-containing layers.
It has also been found that lower hydridosilanes having more than 6, especially 7 to 10, silicon atoms, very particularly those of the formula SinH2n+2, are also incorporated into the laminar structure in the course of conversion in formulations comprising hydridosilane oligomers. For this reason, these compounds, in coating compositions containing hydridosilane oligomers, are unsuitable for production of thin (corresponding to thicknesses less than or equal to 25 nm) and high-quality silicon-containing layers.